1. Field of the invention
The present invention relates to an optical module for two-way transmission.
2. Description of the Related Art
In recent years, research and development of application of an optical transmission system to subscribers systems has been pursued on an implementation level. For example, it is proposed that a two-way optical transmission system through the use of the same wavelength or wavelength multiplex be applied to subscribers systems. The proposed system is such that carries on two-way optical transmission through a single optical fiber linking the station and each subscriber's terminal, and the establishment of technology to mass-produce the optical module for two-way transmission functioning for transmission and reception in the subscribers' terminal devices is one of the key technologies in implementing the system.
The commonest structure to achieve transmitting and receiving functions in a subscriber's device in the subscribers system to which two-way optical transmission can be applied includes an LD module structured so as to converge a light emitted from a laser diode chip into the excitation end of a first optical fiber, a PD module structured so as to converge a light emitted from the excitation end of a second optical fiber into a photodiode chip, and an optical coupler for coupling the first and the second optical fibers to a third optical fiber as the optical transmission path. Since the above mentioned structure is disadvantageous in terms of downsizing and cost reduction, there are proposed optical modules for two-way transmission in which the functions of transmission and reception can be achieved by a single part.
An example of the optical modules for two-way transmission of the related art includes an LD collimator formed by integrating a laser diode chip and a lens, a PD collimator formed by integrating a photodiode chip and a lens, a fiber collimator formed by integrating an end of an optical fiber and a lens, and an optical coupler structured by forming a filter film on a glass substrate. The LD collimator, PD collimator, fiber collimator, and the optical coupler are for example fixed on the substrate in predetermined relative positions. A transmitted light output from the LD collimator is for example reflected by the filter film and input to the fiber collimator, while a received light output from the fiber collimator is for example allowed to pass through the filter film and a glass block and input to the PD collimator.
Another example of the optical modules for two-way transmission of the related art includes a Y-branch type optical waveguide having a first to a third port. The first to third ports respectively have an optical fiber, a laser diode chip, and a photodiode chip, optically connected thereto. A transmitted light from the laser diode is supplied to the optical fiber through the Y-branch and a received light from the optical fiber is supplied to the photodiode through the Y-branch.
With the former related art example of the optical modules for two-way transmission, there was a problem that the downsizing was difficult because the collimators had to be fabricated as separate parts. With the latter related art example of the optical modules for two-way transmission, there was a problem that skill was required in such work as the coupling of the optical fiber with the optical waveguide and, hence, fabrication of it was not easy.